Gate-Tunable Optoelectronic Synapses Based on All-Solution-Derived ZnO/Al ₂ O ₃ /HfO ₂ Thin-Film Transistors for Efficient Neuromorphic Vision Systems

Optoelectronic synapses play a crucial role in the development of neuromorphic computing systems. In this study, the optoelectronic synaptic properties of a thin-film transistor (TFT) that utilizes all solution-derived ZnO/Al 2 O 3 /HfO 2 thin films have been investigated. The device shows a field-effect channel mobility of 29.60 cm 2 ·V −1 ·s −1, an on-off current ratio of 2.3 × 10 8, a threshold voltage of 3.14 V, and a subthreshold slope of 81.23 mV/dec with a drain voltage of 4 V. The optical synaptic properties were studied by applying continuous gate voltages with varying polarity and magnitude. Photo-induced Excitatory Post-Synaptic Current spikes are boosted by gate bias, regardless of polarity. Retention time, however, is extended only with a positive bias. This is due to the rapid separation and trapping of photogenerated carriers under illumination and gate bias. As a result, the device achieves 92.48% recognition accuracy in handwritten digit recognition with a positive gate voltage of 0.5 V. This is higher than 88.83% at −0.5 V and 90.81% without bias. This research provides an alternative way for developing low-cost, high-performance neuromorphic vision perception systems.